Megaupload, one of the largest file-sharing sites in the web, has been shut down by officials in the US. The site’s founders have been charged with violating piracy laws.

Federal prosecutors have accused it of costing copyright holders more than $500m (£320m) in lost revenue. The firm says it was diligent in responding to complaints about pirated material. The news came a day after anti-piracy law protests, but investigators said they were ordered two weeks ago.

The US Justice Department said that Megaupload’s two co-founders Kim Dotcom, formerly known as Kim Schmitz, and Mathias Ortmann were arrested in Auckland, New Zealand along with two other employees of the business at the request of US officials. It added that three other defendants were still at large. In response, hackers targeted the US Department of Justice and FBI websites. The FBI website is intermittently unavailable due to what officials said was being “treated as a malicious act”. The hackers’ group Anonymous said it was carrying out the attacks.

The charges included copyright infringement, conspiracies to commit racketeering, and money laundering. A federal court in Virginia ordered that 18 domain names associated with the Hong Kong-based firm be seized.

Before it was shut down the site posted a statement saying the allegations against it were “grotesquely overblown”. The announcement came a day after thousands of websites took part in a “blackout” to protest against the Stop Online Piracy Act (SOPA) and the Protect Intellectual Property Act (PIPA).